Filament cutting devices have generally taken the form of a power source connected to a shaft which holds a whirling or rotating filament holding head or housing. Within the head or housing is at least one flexible filament that extends exteriorly of the housing. The head or housing is rotated at a speed sufficient to create line rigidity. The whirling filament is employed to cut grass or weeds. As a result of normal usage, the flexible filament often becomes worn, frayed or broken. The effective cutting length of the filament is thereby shortened. It is necessary, therefore, to provide within the filament cutting device a line feed mechanism for uncoiling, paying out or otherwise providing a new cutting length of flexible filament. To avoid overloading the power source and also to conserve flexible filament, it is desirable to have a mechanism which permits the paying out of the filament in predetermined discrete increments only.
Devices are known in the prior art for feeding out a metered length of flexible filament. Some of these require the filament cutting device to be stopped to disengage a locking mechanism to unlatch a filament spool for rotation relative to a filament guide means. With the spool free to rotate, the free end portion of the filament is lengthened by manually pulling it from the spool. These manually-operated devices obviously are not very convenient and usually are quite time-consuming to operate.
Other filament cutting devices need not be stopped while feeding filament. Some of these other cutting devices have line indexing structure remotely operable from the operator's handle. For example, U.S. Pat. No. 4,134,204 shows a remotely operable indexing structure comprised of two sets of axially-displaced and rotationally-offset teeth. A rod extending radially relative to the drive shaft axis and attached to a driving means engages a tooth from one set to drive the spool synchronously with a guide housing. To feed additional filament, the operator remotely causes the rod to move axially, thereby disengaging the rod from the first set of teeth and engaging the second set. The rod when subsequently released by the operator again moves axially to disengage from the second set of teeth and reengage the first set. During this sequence, the rod advances from a driving engagement with one tooth in the first set to a consecutive tooth in rotationally relative to the spool and to feed a discrete amount of filament from the spool. Although remote control structure may be advantageous at times, it makes the device more complex and can be troublesome to maintain.
There are filament cutting devices which utilize the principle of rotational momentum during the deceleration or stopping of the cutting device to advance the spool portion of the device relative to the filament guide means portion. One such device is disclosed U.S. Pat. No. 4,245,454, which is assigned to the assignee of this invention. The line metering device disclosed therein includes a driving mechanism and a driven mechanism. A first set of teeth with ramp elements therebetween is formed on the top of a spool which is preferably coupled directly to the driving mechanism. A second set of teeth for engagement with the first set of teeth is formed on an under surface of a guide drum which is coupled to the driven means and disposed in an overlying relationship with the filament spool. A bias means forces the second set of teeth on the guide drum into driving engagement with the first set of teeth on the filament spool. When the driving means is rapidly braked by a suitable decelerating means, the rotational momentum of the guide drum overcomes the bias force holding the first and second sets of teeth in an engaging relationship and allows the second set of teeth to slide up the ramp means and rotatively move the guide drum relative to the filament spool. The relative rotation of the guide drum and the filament spool results in a lengthening of the swinging portion of the filament. Such a line metering apparatus utilizing the principle of rotational momentum is especially useful on wheeled cutting devices.
Additionally, there are filament cutting devices which have feeding mechanisms operated by bumping the cutting devices on the ground. Such a device is disclosed in the patent application of Henry B. Tillotson entitled "Line Metering Apparatus", filed Aug. 13, 1976, under Ser. No. 714,013 and assigned to the assignee of this invention. The cutting device disclosed in Tillotson has a drive shaft which carries a drive gear having teeth projecting radially outward. A filament spool carries a driven gear having first and second sets of gear teeth which project radially inward for selective engagement with the drive gear teeth. The two sets of driven gear teeth are spaced axially from each other and rotationally staggered a predetermined angular distance. The filament spool is normally axially biased so the drive gear teeth engage the upper set of driven gear teeth. When the free filament end becomes worn or broken, additional filament is fed by tapping the lower surface of the spool on the ground thereby moving the spool axially upward against the bias of the spring until the drive gear teeth move out of engagement with the upper set of driven gear teeth and into engagement with the lower set of driven gear teeth. As this happens, the staggered relation of the driven gear teeth causes limited relative rotational movement of the spool relative to the drive shaft causing a predetermined length of filament to unwind. As the tapping force is removed, the spool returns to its original axial location thereby allowing an additional length of filament to unwind in the same manner.
Tillotson discloses the advantageous means of bumping a feeding mechanism on the ground to feed a discrete amount of filament. Tillotson utilizes the axial movement of drive teeth. The present invention discloses new and unobvious means of feeding line by bumping the feeding mechanism on the ground without such axial movement.